I use a 50 gal breeder tank with a power head and a hob filter. I make sure the new arrivals are eating and then hit them with a round of API general cure and then use cp (new life spectrum ich sheild powder) for 21 days. after that I slowly raise the salinity thru water changes (1-2 weeks) and watch for any signs of infections. retreat if necessary.
Only filter floss or a sponge (depending on the filter your using) I use a Penguin 200, when using medication i run it with the bio-wheel and some filter floss in it and have filters with active carbon on hand to pull the medication out of the water. I also use Seachem prime between water changes to keep the ammonia in check.
Sponge filters are another good option if it's a smaller tank. You can let it run in your sump for a month or so to get it cycled and full of bacteria then it's always ready for a QT tank. As for how long. Ideally 4-6 weeks
You just don't want to put any media from the QT tank back into the display without sterilizing it first
You would also want a small powerhead or job filter for flow
You will also want to get some pvc pipe fittings to give the fish a place to hide and sleep, I use a combination of 1", 1.5",2" and a couple 3" diameter pcs. also take some time and read up on Chloroquine phosphate prior to using it.